Description

Superoxide dismutase (SOD, EC 1.15.1.1) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide (O₂^.-) radical into either ordinary molecular oxygen (O₂) or hydrogen peroxide (H₂O₂). Superoxide is produced as a by-product of oxygen metabolism and, if not regulated, causes many types of cell damage.
SOD catalyzed dismutation of superoxide with the following half-reactions applicable to all the different metal-coordinated forms of SOD:

M⁽ⁿ⁺¹⁾⁺-SOD + O₂^.- → Mⁿ⁺-SOD + O₂
Mⁿ⁺-SOD + O₂^.- + 2H⁺ → M⁽ⁿ⁺¹⁾⁺-SOD + H₂O₂

where M = Cu (n=1) ; Mn (n=2) ; Fe (n=2) ; Ni (n=2).,Zn

In all mammals, and most chordates 3 SOD have been detected: two copper and zinc SOD (SOD1 located in the cytoplasm, SOD2 in the mitochondria), and one MnSOD (SOD3 extracellular).
In plants, there are three SOD classes. FeSOD (homodimer and tetramer found in chlorplast), MnSOD (homodimer and homotetramer mainly found in mitochondrion and peroxisomes) and CuZnSOD (in the chloroplast and cytosol).
In prokaryote, iron or manganes SOD can be found together with Nickel-containing SOD.